As Disasters Go, Hurricanes are Predictable. That’s Not Saying Much.

Over the past few days, Dorian has been – literally – all over the map.

Earlier models suggested that the storm would crash into Puerto Rico and the Dominican Republic as a Category 1 hurricane, losing strength over the rocky terrain it encountered. A couple of days later, the storm had sideswiped Puerto Rico and was cutting a curved path towards Florida, possibly as a Category 3 hurricane.

Thursday morning, the National Hurricane Center announced that Dorian might reach Category 4 status. And while it’s likely to hit the southeastern state on Monday, it’s still not entirely clear which path it will take.

That’s not unique to Dorian, said Corene Matyas, a professor who studies tropical climatology at the University of Florida.

“No two tropical cyclones take the same track,” she said. A storm’s future path depends on a combination of its size, speed, and strength, combined with the complex atmospheric conditions around it. The further out a prediction is, the less likely it is to be accurate.

But in particular, Dorian hasn’t been moving the way scientists expected, said Jhordanne Jones, a graduate researcher at Colorado State University. Despite moving through dry air and dusty particles, which often cause tropical storms to lose strength or even dissipate as they suck in air from their surroundings, Dorian has remained a healthy storm system.

“We’ve had a really quiet season so far. During this time, we usually see the North Atlantic come alive, but there’s also still enough conditions that can suppress hurricane activity this year,” Jones said. “Dorian is still powering through that.”

The secret to Dorian’s continuing strength may have something to do with its size.

“It’s a really compact storm, and that seems to be helping it move through without much interference,” Jones said. “It has a little insulation from the circulation around it.”

It’s likely to get stronger, Jones said, as it moves toward moister air, which tends to help tropical storms intensify.

In addition, there’s not much of a strong flow in any one direction, which makes it harder to predict where the storm will move. “In essence, Dorian is free to move where it pleases,” said Jones.

The change in Dorian’s track seems to be due in part to smaller storms on its eastern side, which have pulled its center off its original course. That change in track meant that Puerto Rico, still vulnerable from Maria, was largely spared, as was the island Hispaniola (where the Dominican Republic and Haiti are  located.)

But it also meant that Dorian didn’t have its anticipated collision with the islands’ bumpy terrain, which would have slowed and weakened it.

The region has spent days in anticipation, but Matyas explained that hurricanes are less predictable than most people realize.

Look at a hurricane map, and you’ll see the projected path of the storm’s movement in a funnel shape that increases in width – often called the “cone of uncertainty” or occasionally (and more dramatically) “the cone of terror.” It’s easy to assume that that cone gives some sense of the size of the storm or of the surrounding danger zone.

That’s just not the case, Matyas said. Instead, “the idea is that there is a 67% likelihood of the storm’s center passing in that cone” (and a 33% likelihood the center of the storm will veer outside of that cone.)

Just looking at a cone of uncertainty won’t give you an idea of how wide the storm’s breadth is, or even much of a sense of who’s in danger.

Being far from a hurricane’s projected center is no guarantee of safety. “The outer edge of the storm can also be very dangerous,” with strong winds, storm surge, and heavy rainfall occurring up to about 200 miles from the center, Matyas said.

What does all this uncertainty mean for the people (possibly) in the storm’s path?

“[Hurricane Dorian] in particular… We really don’t have any certainty on,” said Aniruddha Upadhyay, director of environment of care and safety at Miami Beach Community Health Center.

In some sense, Upadhyay said, that makes preparation more complicated. While a lot can be done to get ready for a storm in advance – everything from organizing staff to transporting temperature-sensitive medications to a safe location – an emergency response can’t fully kick in until there’s definitely an emergency.

Nonetheless, he said, “it’s dynamic right now, but we are prepared. We’re not waiting until there is a hurricane warning.”

Angie Lindsey, a professor of Family, Youth, and Community Services who studies disaster preparedness and recovery at the University of Florida, said the uncertainty is just part and parcel of living in a part of the world that experiencing tropical storms.

“As a Floridian, and I think with a lot of folks that live in the state, you prepare for the worst and hope for the best,” she said.

Besides, much of the work of preparing for a hurricane comes long before a community finds itself in one’s crosshairs.

Pre-positioning vital supplies, having an emergency plan, and installing solar cells or a generator can be done months and even years ahead of a storm.

Part of being well-prepared, Lindsey said, is knowing that there are a lot of unknowns. “We all have to be flexible and reactive to some extent with hurricane season,” she said.

The storm isn’t likely to go near Lindsey’s community, but “we’re still going to prepare, because you never know if one of these storms is going to turn at the last second.”